Abstract
The Boset-Bericha Volcanic Complex (BBVC) is one of the largest stratovolcanoes of the northern Main Ethiopian Rift (MER). However, very little is known about its eruptive history, despite the fact that approximately 4 million people live within 100km of the complex. Here, we combine field observations, morphometric analysis using high-resolution LiDAR data, geochemistry and 40Ar/39Ar geochronology to report the first detailed account of the geological evolution of the BBVC, with a focus on extensive young lava flows covering the two edifices, Gudda and Bericha. These lavas exhibit a bimodal composition ranging dominantly from basaltic rift floor lavas and scoria cones, to pantelleritic trachytes and rhyolite flows at Gudda, and comenditic rhyolites at Bericha. Further, several intermediate compositions are associated with fissure vents along the Boset-Kone segment that also appear to link the silicic centres. We divide the BBVC broadly into four main eruptive stages, comprising: (1) early rift floor emplacement, (2) formation of Gudda Volcano within two main cycles, separated by caldera formation, (3) formation of the Bericha Volcano, and (4) sporadic fissure eruptions. Our new 40Ar/39Ar geochronology, targeting a representative array of these flows, provides evidence for episodic activity at the BBVC from ~120ka to the present-day. We find that low-volume mafic episodes are more frequent (~10ka cyclicity) than felsic episodes (~100ka cyclicity), but the latter are more voluminous. Over the last ~30ka, mafic to intermediate fissure activity might have reinvigorated felsic activity (over the last ~16ka), manifested as peralkaline lava flows and pyroclastic deposits at Gudda and Bericha. Felsic episodes have on average a higher eruption rate (2–5/1000years) and productivity at Gudda compared to Bericha (1–2/1000years). The young age of lavas and current fumarolic activity along the fault system, suggest that the BBVC is still potentially active. Coincident episodic activity within the BBVC and at several rift segments in the MER is observed, and facilitates continental rifting.
Highlights
Volcanism in Ethiopia is thought to have commenced at ~ 60 Ma with a strong pulse of flood basalt activity around ~28–31 Ma associated with the Afar Plume (Hofmann et al, 1997)
Based on the integration of high resolution DEM (LiDAR, Aster), satellite, aerial and Landsat images, field observations and geochemical data, the Boset-Bericha Volcanic Complex (BBVC) can be divided into four main eruptive stages: (1) rift floor basalts, (2) formation of Gudda Volcano in two main cycles (“old” Gudda and Gudda), between which caldera formation occurred, (3) the formation of Bericha Volcano, and, (4) sporadic fissure eruptions recurring between those stages
This bimodal magmatism has been described in previous studies of the BBVC (Di Paola, 1972; Brotzu et al, 1974, 1980, 1981; Ronga et al, 2010; Macdonald et al, 2012), as well as at other Ethiopian rift volcanoes such as Gedemsa (Peccerillo et al, 2003), Fantale (Gibson, 1974) and others (Trua et al, 1999)
Summary
Volcanism in Ethiopia is thought to have commenced at ~ 60 Ma with a strong pulse of flood basalt activity around ~28–31 Ma associated with the Afar Plume (Hofmann et al, 1997). Time constraints of Quaternary volcanism within the northern Main Ethiopian Rift (MER) (Fig. 1) are rare and mainly developed in the context of early hominid evolution (Vogel et al, 2006; Morgan and Renne, 2008; Sahle et al, 2013, 2014; Hutchison et al, 2016a). Detailed age control from high resolution studies to constrain the evolution of individual volcanic complexes is rare and until now only constrained for Aluto Volcano (Hutchison et al, 2016b). Such constraints are vital to understand the role of magmatism within individual volcanic complexes though time during continental rifting
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